Photovoltaic DC-to-AC power converter and control method

• US 7,521,914 B2
• Filed: 01/02/2008
• Issued: 04/21/2009
• Est. Priority Date: 08/10/2005
• Status: Active Grant

• Current Assignee: Schneider Electric Solar Inverters Usa, Inc. (Schneider Electric SE)
• Original Assignee: Xantrex Technology Incorporated (Mission Critical Electronics LLC)
• Inventors: Dickerson, Arthur F., West, Rick
• Primary Examiner(s): HAN, YOUNGHUIE JESSICA
• Application Number:
  US12/006,472
• Publication Number:
  US 20080106921A1
• Time in Patent Office: 475 Days
• Field of Search: 323/225, 323/268, 323/282, 323/283, 323/284, 323/285, 323/351, 323/906
• US Class Current: 323/288
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02M 7/537 using semiconductor devices only, e.g. single switched pulse inverters
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

An apparatus and method of control for converting DC (direct current) power from a solar photovoltaic source to AC (alternating current) power. A novel DC-to-AC power converter topology and a novel control method are disclosed. This combination of topology and control are very well suited for photovoltaic microinverter applications. Also, a novel variant of this control method is illustrated with a number of known photovoltaic DC-to-AC power converter topologies. The primary function of both control methods is to seek the maximum power point (MPP) of the photovoltaic source with novel, iterative, perturb and observe control algorithms. The control portion of this invention discloses two related control methods, both an improvement over prior art by having greatly improved stability, dynamic response and accuracy.

Claims

1. A power converter configured to convert direct current (DC) from a source to alternating current (AC) for supply to an AC line, the power converter comprising:

an energy storage device;

a buck stage configured to regulate voltage on the energy storage device as a function of current sourced into the AC line;

a boost stage configured to be driven by an error between source voltage and a reference voltage; and

a controller configured to incrementally increase the reference voltage until a corresponding decrease in source power results.

2. The power converter of claim 1, wherein the energy storage device is an electrolytic capacitor.

3. The power converter of claim 1, wherein the energy storage device is a plastic film capacitor.

4. The power converter of claim 1, wherein the source is a photovoltaic module.

7. The power converter of claim 1, wherein the source is a photovoltaic module.

5. A method for controlling a DC-to-AC power from a power source to a power line, comprising:

regulating voltage on an energy storage capacitor by an amount of current sourced into the power line;

driving a boost stage based on an error between source voltage and a reference voltage; and

incrementally increasing the reference voltage until a corresponding decrease in source power results.

6. A power converter configured to convert direct current (DC) from a source to alternating current (AC) for supply to an AC line, the power converter comprising:

a buck stage through which power is delivered from the source to the AC line, the buck stage being configured to be driven as a servo loop that includes an error signal that is input to the buck stage, the error signal being a function of a scaling factor derived from a voltage from the source and from a reference voltage; and

a controller configured to incrementally increase the reference voltage until a corresponding decrease in source power results.